The present invention relates to novel oxide anode materials and method of making the same. There is substantial interest from both the Government and Industry in identifying materials for Solid Oxide Fuel Cell (SOFC) anodes. The materials used as an SOFC anode must possess a high electronic conductivity or preferably mixed ionic and electronic conductivity. It is well known that the materials must exhibit sufficient catalytic activity towards the reaction proceeding on the electrode surface to minimize polarization losses. Also necessary are adequate porosity for gas transport, and good chemical and mechanical compatibility with the electrolyte and interconnect. Moreover, the anode must be thermally stable over a wide range of temperatures.
Another desirable feature is that an anode should be stable over a rather wide range of oxygen partial pressures, such as for example, in a low oxygen partial pressure prevalent in the fuel gas inlet as well as in the more oxidizing conditions at the fuel outlet. Furthermore, if the SOFC is to operate on unreformed hydrocarbons, the anode should also possess a high catalytic activity for hydrocarbon oxidation without carbon deposition.
As background to this invention, fuel cell devices are known and used for the direct production of electricity from standard fuel materials including fossil fuels, hydrogen, and the like by converting chemical energy of a fuel into electrical energy. Fuel cells typically include a porous anode, a porous cathode, and a solid or liquid electrolyte therebetween. In operation, gaseous fuel materials are contacted, typically as a continuous stream, with the anode (also referred to as the “fuel electrode” of the fuel cell system, while an oxidizing gas, for example air or oxygen, is allowed to pass in contact with the cathode (also referred to as the “air electrode”) of the system. Electrical energy is produced by electrochemical combination of the fuel with the oxidant. Because the fuel cells convert the chemical energy of the fuel directly into electricity without the intermediate thermal and mechanical energy step, their efficiency is substantially higher than that of conventional methods of power generation.
In a typical SOFC, a solid electrolyte separates the porous metal-based anode from a porous metal or ceramic cathode. Due to its mechanical, electrical, chemical and thermal characteristics, yttria-stablized zirconium oxide (YSZ) is currently the electrolyte material most commonly employed. Currently, the anode in a typical SOFC is made of nickel-YSZ cermet, and the cathode is typically made of doped lanthanum manganites, lanthanum ferrites or lanthanum cobaltites. In such a fuel cell, the fuel flowing to the anode reacts with oxide ions to produce electrons and water. The oxygen reacts with the electrons on the cathode surface to form oxide ions that migrate through the electrolyte to the anode. The electrons flow from the anode through an external circuit and then to the cathode. The movement of oxygen ions through the electrolyte maintains overall electrical charge balance, and the flow of electrons in the external circuit provides useful power. Typical SOFC operate at high temperatures, 650-1000° C. This allows flexibility in fuel choice and results in suitable fuel-to-electricity and thermal efficiencies; however, high temperatures impose stringent requirements on the materials selections for other components of the fuel cell or fuel cell assembly.
U.S. patent application Ser. No. 10/427,866 filed May 1, 2003 (Cerium-Modified Doped Strontium Titanate Compositions for Solid Oxide Fuel Cell Anodes and Electrodes For Other Electrochemical Devices) discloses novel oxide electrode materials comprising of a doped cerium oxide phase and a doped titanium oxide phase and methods for making and using the same and all embodiments and disclosure is hereby incorporated into the present by reference.
For solid oxide fuel cell (SOFC) applications requiring anode stability in oxidizing and sulfur containing atmospheres, doped titanates and doped ceria have been considered as potential candidate materials In particular, samaria- and gadolinia-doped ceria are known to be good electrocatalysts for hydrogen oxidation. Moreover, they are less susceptible to carbon deposition in hydrocarbons than traditional nickel-zirconia anodes for solid oxide fuel cells (Marina, Bagger et al. 1999; Marina and Mogensen 1999). However, doped cerias typically exhibit low electronic conductivity that limits their suitability for anode-supported SOFCs. Donor doping results in increased electronic conductivity compared to pure or acceptor-doped ceria
In view of the above background, it is apparent that there is a continuing need for further developments in the field of SOFC technology. In particular, there is a need for further advancement in the development of alternative anode materials having suitable properties for use in advanced SOFC designs. There is also a need for further advancement in the development of other alternatives electrochemical devices, such as, for example, electrolyzers, electrochemical sensors and the like. The present invention addresses these needs, and further provides related advantages.